1. Field of Invention
The invention relates to a transformer and in particular, to a transformer with fixed pins.
2. Related Art
The transformer is a commonly used voltage converting apparatus for various electronic devices. The transformer and the circuit board of the electronic device are electrically connected via the ends of windings thereof. As shown in FIG. 1, a conventional transformer 1 includes a core set 11, a bobbin 12, a primary winding (not shown) and a secondary winding (not shown). The primary and secondary windings surround the bobbin 12, and have electromagnetic interactions with the core set 11 to achieve voltage conversion. The winding ends of the primary and secondary windings are connected with copper wires 131, 132, 133 covered with PVC films by soldering. The free ends of the copper wires 131, 132, 133 are provided with fixed terminals 1311, 1321, 1331. The copper wires 131, 132, 133 are then connected with the circuit board (not shown) of the electronic device via the fixed terminals 1311, 1321, 1331.
Please refer to FIGS. 2a and 2b. Another conventional transformer 1A has the improved connection of the winding ends illustrated as follows. First, the primary and secondary windings are wound around the bobbin 12. The winding part around the bobbin 12 is covered with an insulating tape 14. There are totally four winding ends 121, 122, 123, 124 pulled out from the primary and secondary windings. The winding end 121 is connected with a copper wire 131a, the winding end 122 is connected with the copper wire 132a, and the winding ends 123, 124 are connected with the copper wire 133a. Therefore, the winding ends 121, 122, 123, 124 are connected with the circuit board (not shown) of the electronic device via the copper wires 131a, 132a, 133a. 
As shown in FIG. 2c, in order to prevent the copper wires 131a, 132a, 133a from direct contact with each other and to prevent short circuits and thus burning of the transformer 1A because the soldering points pierce the PVC insulating films, the conventional transformer uses tapes and pads to separate the exposed parts of copper wires and the soldering points. The copper wire 131a connected with the winding end 121 is bent upward and applied with one or several layers of insulating tapes 14 and a pad 15, thereby covering the exposed and soldering parts of the copper wire. The other winding ends 122, 123, 124 and the corresponding copper wires 132a, 133a can be processed in the same way. Therefore, the copper wires 131a, 132a, 133a can be fixed and organized to prevent wire intertwining and short circuits.
Nevertheless, the drawbacks of the conventional transformers are as follows. The transformer 1A requires a lot of tapes and pads. The circuit board for fixing and organizing wires does not have any function other than insulation. This complicates the structure of the transformer 1A and increases its costs. Moreover, the involved processes of taping and inserting pads lower the yield. Since the winding ends 121, 122, 123, 124 need to be connected to the corresponding copper wires 131a, 132a, 133a by soldering, the quality of the transformer 1A can be lowered due to the piercing problem at soldering points. Moreover, the PVC has a lower melting point (about 105° C.), so the transformer 1A using the copper wires covered with PVC is thus susceptible to heat.
As shown in FIG. 3, another conventional transformer 2 includes a core set 21, a bobbin 22, a primary winding 231, a secondary winding 232 and several pins 241, 242, 243, 244, 245. The primary winding 231 and the secondary winding 232 have several winding ends. The pins 241, 242, 243, 244, 245 are fixed to the bobbin 22 and connected with the winding ends before they are electrically connected with the circuit board. However, when the bobbin 22 forms the pins 241, 242, 243, 244, 245, they can only be fixed at fixed positions of the bobbin 22. It is only applicable to a single specification of bobbin and circuit board. The pins 241, 242, 243, 244, 245 are not flexible in configuration. In addition, when the ends of the transformer 2 are electrically connected with the pins 241, 242, 243, 244, 245, it is likely to have short circuit when the transformer 2 is inserted into a circuit board because the exposed ends are not insulated.
Therefore, it is an important subject to provide a transformer with fixed pins that can improve the above-mentioned drawbacks.